Since 2001, there has been an explosive growth of scientific interest in the role of surface plasmons in optical phenomena including guided-wave propagation and imaging at the subwavelength scale, nonlinear spectroscopy and ‘negative index’ metamaterials. The unusual dispersion properties of metals enable excitation of propagating surface plasmon modes away from the plasmon resonance and near the plasmon resonance enables excitation of localized resonant modes in nanostructures that access a very large range of wavevectors over the visible and near infrared frequency range. Both resonant and nonresonant plasmon excitation allows for light localization in ultrasmall volumes in metallodielectric structures.
To date, little systematic, comprehensive thought has been given to the question of how plasmon excitation and light localization might be exploited to advantage in photovoltaics. Conventionally, photovoltaic absorbers must be optically ‘thick’ to enable nearly complete light absorption and photocarrier current collection. They are usually semiconductors whose thickness is typically several times the optical absorption length. For silicon, this thickness is greater than 50 microns, and it is several microns for direct bandgap compound semiconductors. High efficiency cells must have minority carrier diffusion lengths several times the material thickness. Thus conventional solar cell design and material synthesis considerations are strongly dictated by this simple optical thickness requirement.
Thus there is a need for systems and methods that both enhance photovoltaic performance and reduce cost by using reduced amounts of inexpensive material.